The present invention relates to an apparatus and a method for sterilizing containers and in particular plastic containers. It is known from the prior art that containers are sterilized prior to being filled, particularly when being filled with certain sensitive beverages. Various procedures are known for the purpose of this sterilization, such as, for example, applying a sterilizing medium such as peracetic acid or hydrogen peroxide. More recently, however, efforts have been made to reduce the use of such chemicals.
In general, however, the sterilization of containers is, besides the actual filling operation, the main process step in a, particularly aseptic, bottling system, wherein hereinbelow containers will be understood to mean both finished containers, such as plastic containers or glass bottles, and for instance plastic preforms which are to be expanded into bottles. When disinfecting the containers by means of beams, particularly electron beams, firstly the reliability of the treatment, i.e. the sterilizing effect on each individual container, is important. Another important criterion, however, is also the safety of the operators and staff on the system, particularly since undesired side effects, such as X-ray radiation, occur when applying, for example, electron beams.
As mentioned, when irradiating the containers with high-energy electrons, X-ray radiation also occurs as an undesired side effect. In order to protect the staff and also electronic components in the environs of the machine against this radiation, usually shields are fitted which are made of a material having a sufficient wall thickness. For electron beams having an energy in the region of 150 keV, lead walls having a thickness of 5-12 mm are required for shielding the X-ray radiation (this also depends on the current). As an alternative, a different material can also be used, such as steel for example, but the shielding effect of steel is much lower and therefore the wall thickness must accordingly be thicker.
In any case, the entire system is shielded such that, for the defined radiation parameters and when the system is used as intended, i.e. during normal operation, a residual radiation of more than 1 μSv/h cannot occur at any point outside the system. However, a malfunction may also occur if, for example, one or more of the emitters is defective or is controlled incorrectly, so that increased radiation is produced. In order to ensure this intended or “normal” operation, use is made of detectors and/or sensor devices. A monitoring of this radiation by means of X-ray detectors is known from the internal prior art.
These sensor devices or radiation detectors have to function reliably over many operating hours since they ultimately monitor the radiation safety of the machine and if necessary trigger an emergency stop. During normal operation, the scenario of excess radiation generally does not occur, so that the sensors detect no malfunction and do not trigger an emergency stop for days, weeks or months. It is therefore necessary to check the functioning of the sensor devices at regular time intervals. Several possible ways of doing this are known from the prior art.
In one procedure, the sensitivity of the sensor can be electronically increased, and/or the measurement signal thereof can be additionally amplified. The evaluation of the signal shows a radiation level that is supposedly too high, which must lead to the emitters being switched off. Another checking option lies in exposing the sensor to an increased radiation level so that it has to switch off the radiation sources where necessary, depending on its task. In the simple case, this could be achieved by increasing the normal radiation level inside the machine. However, this should be avoided for reasons of radiation safety. However, both of the aforementioned possibilities have the disadvantage that the system is manipulated and that safety-critical components of the machine are altered. The sensor, the sensor electronics and also the evaluation unit are part of a safety technology.
The object of the invention is therefore to enable such monitoring of the systems without to this end carrying out the manipulations, necessary in the prior art, on safety-critical components.